The present invention relates to the field of communication networks, and, more particularly, to mobile ad hoc wireless networks and related methods.
A rapidly developing area of wireless networks is mobile ad hoc networks. Physically, a mobile ad hoc network includes a number of geographically-distributed, potentially mobile nodes wirelessly connected by one or more radio frequency channels. Compared with other type of networks, such as cellular networks or satellite networks, the most distinctive feature of mobile ad hoc networks is the lack of any fixed infrastructure. A pure mobile ad hoc network is formed of mobile nodes only, and a network is created on the fly as the nodes transmit to or receive from other nodes. Node movement patterns may be anywhere from continuous to start-stop type patterns. The network does not in general depend on a particular node and dynamically adjusts as some nodes join or others leave the network.
An ad hoc network can be quickly deployed and provide much needed communications. Ad hoc networks will allow people to exchange data in the field or in a class room without using any network structure except the one they create by simply turning on their computers or PDAs, for example.
New applications for mobile ad hoc networks will continue to emerge and become an important part of the communication structure. Due to the lack of a fixed infrastructure, nodes must self-organize and reconfigure as they move, join or leave the network. All nodes could potentially be functionally identical and there may not be any natural hierarchy or central controller in the network. Many network-controlling functions are distributed among the nodes. Nodes are often powered by batteries and have limited communication and computation capabilities. The bandwidth of the system is usually limited. The distance between two nodes often exceeds the radio transmission range, and a transmission has to be relayed by other nodes before reaching its destination. Consequently, a network has a multihop topology, and this topology changes as the nodes move around.
The Mobile Ad-Hoc Networks (MANET) working group of the Internet Engineering Task Force (IETF) has been actively evaluating and standardizing routing, including multicasting, protocols. Because the network topology changes arbitrarily as the nodes move, information is subject to becoming obsolete, and different nodes often have different views of the network, both in time (information may be outdated at some nodes but current at others) and in space (a node may only know the network topology in its neighborhood usually not far away from itself).
A routing protocol needs to adapt to frequent topology changes and with less accurate information. Because of these unique requirements, routing in these networks is very different from others. Gathering fresh information about the entire network is often costly and impractical. Many routing protocols are reactive (on-demand) protocols: they collect routing information only when necessary and to destinations they need routes to, and do not generally maintain unused routes after some period of time. This way the routing overhead is greatly reduced compared to proactive protocols which maintain routes to all destinations at periodic time intervals. It is important for a protocol to be adaptive. Ad Hoc on Demand Distance Vector (AODV), Dynamic Source Routing (DSR) and Temporally Ordered Routing Algorithm (TORA) are representative of on-demand routing protocols presented at the MANET working group.
Examples of other various routing protocols include Destination-Sequenced Distance Vector (DSDV) routing which is disclosed in U.S. Pat. No. 5,412,654 to Perkins, and Zone Routing Protocol (ZRP) which is disclosed in U.S. Pat. No. 6,304,556 to Haas. ZRP is a hybrid protocol using both proactive and reactive approaches based upon distance from a source node.
These conventional routing protocols use a best effort approach in selecting a route from the source node to the destination node. Typically, the number of hops is the main criteria (metric) in such a best effort approach. In other words, the route with the least amount of hops is selected as the transmission route.
Existing communication node advertisement and communication node neighbor discovery approaches including those for ad hoc networks, only use network-condition-independent mechanisms such as constant transmit rate or random transmit rate xe2x80x9chelloxe2x80x9d messages from nodes to announce, or advertise, their presence. These transmitted announcements are called xe2x80x9cbeaconsxe2x80x9d and conventional approaches do not endow these beacons with any degree of intelligence. Other nodes may detect these beacons and either form a network from scratch, add the newly-detected node to the existing network, or disallow further communications to this newly-detected node.
In view of the foregoing background, it is therefore an object of the present invention to provide the general framework, called the xe2x80x9cIntelligent Communication Node Object Beacon Frameworkxe2x80x9d (ICBF), for intelligent, adaptive advertisement by any communications node object of its presence and/or the corresponding detection (neighbor discovery) by another node object or the network of those node objects transmitting such beacons.
This and other objects, features, and advantages in accordance with the present invention are provided by a method for detecting variable beacon signals in a mobile ad hoc network. The network includes a plurality of wireless mobile nodes and a plurality of wireless communication links connecting the nodes together. Each of the mobile nodes transmits node condition information using the variable beacon signals, which are varied based upon a node condition. The method includes searching for the variable beacon signals at a given mobile node using an initial detection rate and at an initial detection frequency, and increasing a detection rate from the initial detection rate up to a maximum detection rate while searching for the variable beacon signals at the initial detection frequency.
The maximum detection rate may be predetermined or set according to a received maximum detection rate transmitted by a neighboring mobile node. Also, the detection rate may be increased according to a function defining time varying properties of the variable beacon signal of a neighboring mobile node. The variable beacon signals may vary in at least one of transmission rate, transmission frequency and transmission pattern, and the method may include changing a detection frequency from the initial detection frequency while searching for the variable beacon signals.
The node condition may include node movement, and the transmission rate of the variable beacon signal is increased based upon increased node movement and decreased based upon decreased node movement. The node movement may be node velocity, node acceleration and/or node movement pattern. The node condition may also include quality of service (QoS) or priority of information, and the transmission rate, the transmission frequency and/or the transmission pattern of the variable beacon signal may be varied based upon changes in QoS or priority of information. The transmission rate of the variable beacon signal does not exceed a transmission rate threshold based upon available bandwidth.
The method may also include determining a type of variable beacon signal being transmitted from a neighboring mobile node by processing beacon signal information received from the neighboring mobile node via a beacon properties signal.
Another aspect of the present invention is a mobile ad hoc network including a plurality of wireless mobile nodes connected by a plurality of wireless communication links. Each mobile node having a communications device to wirelessly communicate with other nodes of the plurality of nodes via the wireless communication links, and a controller to route communications via the communications device. The controller including a beacon signal generator to generate and transmit node condition information using a variable beacon signal which are varied based upon a node condition, and a beacon signal detector to search for the variable beacon signals at a detection rate, which is increased from an initial detection rate up to a maximum detection rate, and at an initial detection frequency.
The maximum detection rate may be predetermined or based upon a received maximum detection rate transmitted by a neighboring mobile node. The beacon signal detector may increase the detection rate according to a function defining time varying properties of the variable beacon signal of a neighboring mobile node. Also, the beacon signal generator preferably varies the variable beacon signal by varying at least one of transmission rate, transmission frequency and transmission pattern. The beacon signal detector may change a detection frequency from the initial detection frequency while searching for the variable beacon signals.
The beacon signal generator may increase the transmission rate of the variable beacon signal based upon increased node movement and decrease the transmission rate based upon decreased node movement. Also, the beacon signal generator may transmit beacon signal information using a beacon properties signal to advertise a type of beacon signal being transmitted to the plurality of nodes of the mobile ad hoc network, while the beacon signal detector determines a type of variable beacon signal being transmitted from a neighboring mobile node by processing beacon signal information received from the neighboring mobile node via the beacon properties signal.